Since the tag_8021q tagger is software-defined, it has no means by
itself for retrieving hardware timestamps of PTP event messages.

Because we do want to support PTP on ocelot even with tag_8021q, we need
to use the CPU port module for that. The RX timestamp is present in the
Extraction Frame Header. And because we can't use NPI mode which redirects
the CPU queues to an "external CPU" (meaning the ARM CPU running Linux),
then we need to poll the CPU port module through the MMIO registers to
retrieve TX and RX timestamps.

Sadly, on NXP LS1028A, the Felix switch was integrated into the SoC
without wiring the extraction IRQ line to the ARM GIC. So, if we want to
be notified of any PTP packets received on the CPU port module, we have
a problem.

There is a possible workaround, which is to use the Ethernet CPU port as
a notification channel that packets are available on the CPU port module
as well. When a PTP packet is received by the DSA tagger (without timestamp,
of course), we go to the CPU extraction queues, poll for it there, then
we drop the original Ethernet packet and masquerade the packet retrieved
over MMIO (plus the timestamp) as the original when we inject it up the
stack.

Create a quirk in struct felix is selected by the Felix driver (but not
by Seville, since that doesn't support PTP at all). We want to do this
such that the workaround is minimally invasive for future switches that
don't require this workaround.

The only traffic for which we need timestamps is PTP traffic, so add a
redirection rule to the CPU port module for this. Currently we only have
the need for PTP over L2, so redirection rules for UDP ports 319 and 320
are TBD for now.

Note that for the workaround of matching of PTP-over-Ethernet-port with
PTP-over-MMIO queues to work properly, both channels need to be
absolutely lossless. There are two parts to achieving that:
- We keep flow control enabled on the tag_8021q CPU port
- We put the DSA master interface in promiscuous mode, so it will never
  drop a PTP frame (for the profiles we are interested in, these are
  sent to the multicast MAC addresses of 01-80-c2-00-00-0e and
  01-1b-19-00-00-00).
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>